1. Field of the Invention
The invention relates to a method for producing high-purity silicon, silicon produced according to the method, and silicon fusible in a particular manner.
2. Background Art
Methods for producing high-purity silicon have been known for a long time. The Prime Poly silicon resulting from said methods is because of its production process a compact material which is used in the form of rodlets, approximately spherical granules or irregular solid pieces of silicon. Said materials have because of their compact structure very good melting properties, because of the slow thermal precipitation a high purity, and because of the high volume/surface ratio only slight surface impurities, which are incorporated in the melt. Disadvantages of the existing methods are a very high specific energy consumption per kilogram of pure silicon and, because of the slow precipitation rate, the high costs of manufacture.
In many of the methods for producing Prime Poly silicon investigated in the past, and in the production methods currently used industrially, apart from the silicon deposited on a hot surface, powdery silicon is mainly obtained in the gas phase, in particular when monosilane is used. Because of its high content of impurities, poor handling properties and poor melting characteristics, said powdery silicon was not able to be used to date in the photovoltaic and semiconductor industry. A targeted development of a suitable method for producing silicon in the form of silicon powder is described in the literature. Because of the unfavourable melting characteristics of silicon powder, it was proposed that silicon powder be converted directly into a silicon melt and allowed to solidify in the form of silicon granules, in order to act in said form as the starting material for the production of silicon blocks or silicon crystals (U.S. Pat. No. 4,354,987).